This invention relates to silver halide photographic materials, in particular to magenta dye-forming pyrazolotriazole couplers useful in silver halide photographic materials, and more particularly to pyrazolotriazole couplers which have increased coupler activity as compared to conventional pyrazolotriazole couplers, while having low fog and good dispersability.
Pyrazolotriazole couplers are known to be useful for forming color images in photographic silver halide materials. While these couplers provide good hues, they suffer from a number of problems. Particularly, the photographic activities of these couplers tend to be low. The coupling activity of an image coupler in a photographic film is a measure of its coupling rate with oxidized developer during the silver development stage. In a color negative film, a rapid rate of depletion of image coupler results in lower granularity, which is a desirable trait for fast layer applications.
It is known to improve this activity by attaching a water soluble carboxyl group to the pyrazolotriazole. See, for example, U.S. Pat. Nos. 4,835,094 and 4,791,052. The carboxy-solubilized pyrazolotriazole couplers show improved activity, but tend to be difficult to disperse during the coating process. It is important to have a coupler with good dispersion during the film/paper manufacture as well as for photographic performance. A stable, fine dispersion reduces melt-hold problems during coating operation, producing uniform products with no detectable dispersion granularity. Furthermore, these couplers undesirably give high silver fog during processing. Silver fog or chemical fog is the phenomenon which occurs when silver grains are developed during development in the area that has received no exposure of light. This often causes higher minimum density, higher low-scale granularity, and lower method photographic speed.
It is further known to use sulfonamide solubilizing groups with pyrazolotriazole couplers. See U.S. Pat. No. 4,865,963. However, these couplers are not very active.
Hence there is a need to find a magenta image dye-forming pyrazolotriazole coupler which has high activity, good dispersability, and which gives low fog during development.